Flame-viewing windows are provided for many applications, of which perhaps the most significant is the use of the window to separate a flame side of a structure from another side or to permit viewing of a combustion chamber and, especially, the flame within this combustion chamber. Such windows can be provided on boilers, reactors, heaters or other apparatus in which a flame is produced and where viewing of this flame may be desired, simply to determine whether the flame is on or is satisfactory, for control of combustion parameters, for monitoring flame temperature, or for any other reason which may require frequent or infrequent viewing of the flame.
Flame safety glasses may be used as panes for such windows and a particularly effective glass-ceramic pane is described in German Open Application--DE-OS No. 24 13 552, for example. This high grade expensive pane is held in place all around its periphery by heat-insulating means and has been found to be highly stable although the high cost of the assembly has prevented widespread acceptance and application of such windows.
Lower cost lime-soda-silicate glasses (soda-lime glass) have been avoided because they have been associated with the development of high stresses when subjected to use in the manner described and hence special methods of anchoring panes of this type of glass have been developed as shown, for example, in German Printed Application DE-AS No. 23 44 459 to position the panes in the manner enabling the distortion thereof without breakage.
In general such means only retains the pane at limited locations about the periphery thereof. Thus, while the panes of this latter approach are less expensive, the higher cost and complexity of the frame has created problems. Up to now both methods have proved to be unsatisfactory and unacceptable in many cases.